The purpose of this study is to determine the efficacy of intravenous Cordox (fructose-1, 6-diphosphate) as adjunct therapy to parenteral narcotic analgesia (PNA), determine the lowest dose of intravenous Cordox that is significantly superior to placebo-PNA, and confirm the tolerability of multiple dose exposure to intravenous Cordox in sickle cell patients with painful vaso-occlusive episode.